This invention relates to dust collectors for cleaning particle-laden air, and especially to the type of dust collector that utilizes a plurality of vertically supported filter bags from which accumulations of dust can be shaken loose at certain time intervals when the system is not operating. More particularly, the invention relates to two unique design features adapted for use in such dust collectors, one of which deals with the adjusting of the amplitude of the shaking motion used periodically to remove the dust accumulations in the filter bags and the other of which deals with an improved means for initially distributing the particle-laden air in proper proportion to the lower ends of the filter bags.
In certain commercial operations and processes, such as sand blasting, abrasive cleaning, grinding, and others, dust and other solid particles are produced that must be removed from the atmosphere in order to protect the workman and equipment. The dust collecting equipment that is often used for this purpose has a housing with a series of elongated filter bags mounted therein and the air to be cleaned is passed through the walls of the bags, the solid particles being deposited on the interior surface of the bag. In order to keep the bags relatively clean to realize the desirable efficiency, the bags are usually shaken or agitated at proper intervals to remove the accumulations of dust. The accumulations are usually collected in a hopper below and removed from he housing.
In dust collectors of this type, it is desirable that the air be passed to the filter bags in a smooth, uniform manner, with a minimum of friction loss, and in such a way that the larger and heavier particles are thrown out of the flow path prior to the passage of air through the bags.
The individual filter bags are normally suspended from a hook or other means of suspension connected to a mechanism which is capable of shaking the bags with a back and forth motion, such as a swinging or arcuate motion. It is well known in the art that speed, stroke, span, and excursion of the bag support member during the shaking operation have a material effect on the bag cleaning process. Increase in stroke or excursion bears a linear relationship to the bag cleaning operation.
In a typical shaker mechanism for imparting the desired shaking motion to the filter bags to dislodge particles, the bags are positioned in parallel rows and the upper ends are connected by hooks or the like to pivot shaft assemblies which are oscillated back and forth when the shaking action is accomplished. Usually, a row of bags is located at each side of the pivot shaft assembly so that two rows of bags can be shaken simultaneously. The pivot shaft assemblies generally have a crank arm that is moved to and fro by links which may be connected to two or more crank arms of the pivot shaft assemblies. The links are operatively connected to some type of eccentric crank mechanism which is operatively associated with a drive motor.
Particulates that are filtered out of the air stream form a dust cake on the filter medium. The cake varies in weight and depth, dependent on several factors including dust particle size and density. A small amount of cake improves filter efficiency by reducing permeability in the filter medium. A large amount of cake tends to restrict air flow through the filter, and a portion of the cake must be removed on some regular schedule. If cleaning of the filter medium is too vigorous, all of the dust cake may be removed, with a temporary loss in dust capture efficiency and with undue stresses in the filter material. If cleaning is not vigorous enough, there will be a continuing buildup in dust cake with restrictions to air flow.
The amplitude of cleaning action must be adjustable to compensate for changes in size and physical properties of the dust particles. The amplitude of cleaning must also be adjusted to suit the filter medium as this material varies in weave and weight and finish. An open weave of rough texture will not release the dust cake as readily as a dense weave of smooth texture. The prior art does not provide for easy adjustment of the shaker mechanism to suit these variables.
Another problem encountered with prior art devices is the unequal distribution of incoming dust and air to the plurality of filter bags that compose a dust collector unit. Normal practice is to have a single inlet for the dusty air stream. This system supplies a major amount of air and dust to the nearest bags and a minor amount to those in a far corner. Filter bags receiving the heaviest load will be less efficient and will show abrasion of filter material and a short life span. Filter bags with a small portion of dust and air will be most efficient and have the longest life span. In addition, the travel time for a dust particle to the nearest filter bag does not allow time for heavy particles to settle out by gravity before reaching the filter bag.
The apparatus of the present invention provides for reducing the entering air velocity to a level where heavy particles are released by gravity before reaching the filter medium. This apparatus divides the incoming air stream into two ducts that extend across the inlet chamber. Air velocities are reduced in the twin inlet ducts, and each duct is fitted with a plurality of nozzles that distribute the dusty air at a uniform low velocity toward the filter bags. The spacing of inlet ducts and nozzles ensures that each filter bag receives an equal amount of dust and air. Dust capture efficiency is enhanced by distributing the dust load uniformly, and abrasion of the filter medium is reduced by lower velocities and less dust.
The apparatus of the present invention, however, minimizes the difficulties indicated above and affords other features and advantages heretofore not obtainable.